After a wellbore is drilled, an underreamer may be used to enlarge the diameter of the wellbore. In an underreaming operation, the underreamer is run into the wellbore in a retracted state. In the retracted state, cutter assemblies on the underreamer are retracted inward such that a diameter of the underreamer is less than that of the surrounding casing or wellbore. Once the underreamer reaches the desired depth in the wellbore, the underreamer is actuated into an expanded state. In the expanded state, the cutter assemblies move radially-outwardly, and into contact with the wellbore wall. The underreamer and cutter assemblies are then moved longitudinally within the wellbore to increase the diameter of the wellbore over a desired length of the wellbore.
Conventional underreamers have cutter assemblies that are adapted to increase the diameter of the wellbore by up to about 25% from the original (i.e., pilot hole) diameter. If a larger increase in the wellbore diameter is desired, a first underreamer is run in the wellbore. When the operation is complete, the first underreamer is pulled out of the wellbore and a second, larger underreamer is run into the wellbore to further increase the diameter of the wellbore. Running multiple underreamers into a wellbore is a time-consuming process, which leads to an increased number of downhole trips, and a corresponding increase in costs.